I don’t think my mental image of a chicken sandwich is the same as yours, but I do enjoy an open faced tuna melt, which I find is easier to eat with a knife and fork. But I don’t really consider that a sandwich, either. It’s more like chipped beef on toast, which I suppose you could argue is also a sandwich.
I’d presume you’d eat it like a hot chicken sandwich, ie fork and knife.
I don’t think my mental image of a chicken sandwich is the same as yours, but I do enjoy an open faced tuna melt, which I find is easier to eat with a knife and fork. But I don’t really consider that a sandwich, either. It’s more like chipped beef on toast, which I suppose you could argue is also a sandwich.